Turbo-machines are known to include rows or stages of stationary airfoils, commonly called vanes or stationary blades, inter-spaced between stages of rotating airfoils, commonly called blades. Turbo-machines are known to include an outer casing, a blade ring affixed to the casing, and a plurality of stationary blades affixed to the blade ring, as shown in U.S. Pat. No. 4,699,566, dated Oct. 13, 1987. As a working fluid passes through the turbine, a wake is formed in the working fluid by a first stage of vanes. This wake is known to pass through the following rotating stage of blades and on to the second stage of vanes. Similar interaction occurs between subsequent stages of the machine.
U.S. Pat. No. 5,486,091 dated Jan. 23, 1996, teaches that the relative positioning of two rows of vanes, also known as the clocking of the vanes, can affect the efficiency of a turbine engine.
The clocking effect is known to exist in various types of turbo-machines, including steam turbines, gas or combustion turbines and compressors. U.S. Pat. No. 5,681,142 dated Oct. 28, 1997, teaches that there exists a class of vibratory modes known as the clocking modes in the stator of a compressor. This patent teaches that there is a need to dampen and/or to minimize the magnitude of these clocking mode forces.
It is known to provide for the adjustment of the stationary blades of a gas turbine, as taught in U.S. Pat. No. 5,215,434 dated Jun. 1, 1993. That patent shows an apparatus for adjustment of the pitch of the vanes, i.e. the angle of attack of the airfoil relative to the direction of flow of the working fluid. It does not, however, teach or suggest an apparatus for adjusting the clocking of the stationary vanes.
The above mentioned U.S. Pat. Nos. 4,699,566; 5,486,091; 5,681,142; and 5,215,434 are incorporated by reference herein.
As turbine and compressor designs advance, there is a need to ensure that the optimum clocking is achieved in each machine in order to maximize the overall efficiency of the machine. Further, there is a need to adjust the clocking of stationary vanes in a machine subsequent to the initial operation of the machine in order to affect the efficiency and/or the vibration characteristics of the machine.